Equations of physics about change are written with regard to a variable called ‘time’. Newton’s equations of motion, as prime example, describe how things will change in time. Given the past they will predict what happens in the future. More precisely, after measuring some variables, for example the position and speed of an object, the angle of a swinging pendulum etc, one may use the equations of physics to predict the evolution of these variables with time.
In reality, however, one never measures time itself; The business of physicists is to measure physical variables (oscillations, beats, and many other things) and compare one variable with another. One may count how many beats for each oscillation; how many oscillations for every tick of a stopwatch; how many ticks of the stopwatch between intervals of the standard clock …. By this procedure one derives how the variables change in relation of each other to explain phenomena observed in the world.
As it turns out, it is extremely useful to imagine that a variable called ‘time’ exits which underpins all those movements, even if we cannot measure it directly. In the words of the Greek philosopher Anaximander: “Things are transformed one into another according to necessity, and render justice to one another according to the order of time”. Science has developed since by understanding how phenomena occur according to the order of time. The concept of a time which flows by itself, and in relation to which all things evolve, is a useful one, but not necessarily a concept of nature.
- Newton asserts explicitly in the Principia that we can never measure ‘true’ time but, if we assume that it exits, we can set up an efficient framework to describe nature.
- Belief in the existence of points of time give science extra power to explain, describe, predict, and enrich our understanding.